1. Field of the Invention
The present invention relates to an exhaust gas recirculation (EGR) device for an internal combustion engine, such as a diesel engine for an automobile.
2. Description of the Prior Art
In general, EGR is carried out in order to reduce the amount of NO.sub.x in the exhaust gas of a diesel engine. Since excessive EGR causes smoke, it is desirable to control the EGR precisely in accordance with the engine running conditions.
It has been known that since the difference between the upstream pressure and the downstream pressure of the EGR valve of a diesel engine is smaller than that of a gasoline engine and since the range of control of the amount of EGR is relatively large, the precision of control of the opening degree of the EGR required for a diesel engine is not particularly high and, accordingly, the structure of EGR system can be considerably simplified.
In the prior art system, the engine rotational speed and the engine load are detected by sensors, an electric actuator is driven by signals from the sensors, and negative pressure regulated by the action of the electric actuator is led to a diaphragm chamber of the EGR valve for suitable control of EGR.
In this system, electric control signals are converted into changes of the opening degree of the EGR valve by means of a constant pressure valve with a solenoid and an EGR valve with a diaphragm chamber.
The prior art system of EGR of a diesel engine, however, is not satisfactorily simplified in structure.